Rob, no particular reason I don't use carbon besides the minimal expense. I find that my tanks are clear enough for my viewing pleasure. I did purchase bulk activated carbon from a OCA club member a few years ago and tried some in one of my tanks and didn't notice any difference so I sold the remaining 1.5 lbs at club auctions. However if one should ever use medications in a tank, it would come in handy to remove any remaining meds.
I'm about 15 minutes away from Big Rich and attended a local club visit there a couple months ago before he started the upgrade on his pool conversion to fish pond. Nice guy and doing the best he can for the fish he keeps.